1. Technical Field
This invention relates to telemetry and remote control techniques on a mass-deployed scale, in particular, by sharing the use of subscriber loops of the switched telephone network in a "background" mode for communication services that do not need the participation of the subscribers.
2. Description of the Related Art
In establishing a communication link between two parties, alerting signals are first initiated by the originating party. Once the receiving party responds, some kind of hand-shaking processes take place to identify, greet and synchronize the two parties before the actual information exchanges start. Depending on the complexity of a system involved, this process could be very simple, or very complicated, and is generally referred to as "communication protocol".
When a communication facility is set up by a third-party service provider, the protocol becomes much more rigorous because of the need to protect the privacy between the two communicating parties as well as to assure the proper financial reward to the service provider. One classical service provider is the switched telephone network. A telephone switch applies, based on the destination information given by the originating ("calling") subscriber, ringing signals toward the receiving instrument. Upon answering by the subscriber at the termination (the "called" party), a connection is established. Traditionally, the telephone company charges the calling party for the duration when the connection is maintained, that is, from the moment that the called party answers the call to the instant that the connection is taken down. Based on this rule, it is clear that, for the interest of the telephone company, it is important to prohibit information exchange between the two end subscribers until a definitive "answer" event is established.
This communication protocol has worked well in providing the conventional telephony services which has been evolved into the largest communications network currently in existence--the Public Switched Telephone Network (PSTN). However, because the fundamental goal of the telephone service provider is to make the called subscriber answer the phone, ringing is always the first signal that arrives at the called subscriber's instrument. Even with the latest enhanced calling service feature--the Caller IDentification, signals that identify the caller are sent toward the called instrument during the silent period of the ringing cycles. Therefore, in the existing PSTN which is originally intended for voice communication services, bell ringing is always the first indication of an incoming call, regardless of the type of the caller.
The question is, "Can the ringing be suppressed for certain types of calls that are destined for an instrument, not a human being, so that the subscriber will not be disturbed?" With the majority of the subscriber loops idle most of the time, this capability would open up the possibilities of utilizing these resources for new communications that do not need subscribers' involvement.
Nevertheless, there is a stumbling block that stands in the way. Because the PSTN is a well established facility, attempts to modify its existing operation procedures, such as the call setup protocol, should meet great resistance and difficulties, if not an impossibility. So, the next question should be: "What can be done to achieve a connection with a call which will not sound the ringer in the terminating instruments, even though every call actually is preceded with the ringing signals?"
With the deep penetration of the PSTN into almost every corner of the modern society, the potential of such a capability which would provide communications between data instruments in addition to traditional voice calls between human subscribers, hereof named as Telemetry and Remote Control (TRC), can be enormous.
One special example of the TRC applications is the simple one-to-one communications between data type instruments such as computer modems and facsimile transmission equipments over the telephone line originally set up for simple voice calls. A commercially available device, generally referred to as the "FAX Switch", has been able to distinguish a FAX or modem call from a voice call by recognizing special pilot tones emitted by the calling FAX or modem. However, it is a specific solution for a specific type of equipment and it actually has to perform this discrimination function only after answering to the ringing signal. Thus, without choice, any call made to a line with this type of instruments would always pay extra fee to the telephone company for the duration of screening and routing the call after answering without being alerted to such a fact.
The technique disclosed in this invention is of a generic nature that it can not only replace the need of a dedicated equipment such as the FAX switch but also avoid causing the ordinary caller to pay extra fee.
Another example of TRC is the utility meter reading and load distribution control. In this case, the configuration is a network connecting several parties (different utility companies) to many parties (the mass customers) with each communication session being a one-to-one connection. Thus, a general connection scheme is required.
The utility companies have long been facing the cost, convenience, frequency and accuracy issues of meter reading. Methods of meter reading that are non-interfering to the customer, yet capable of maintaining an accurate and cost-effective operation, have been sought for during the past two decades. Various techniques have been in trials. These range from power line data transmission to radio link polling. Each approach has its special characteristics and limitations. None of them seems to meet all those issues that started this new field, commonly known as Automatic Meter Reading (AMR).
While AMR is originated from utility companies' interests in cutting cost, the long term implication of this effort is actually far more reaching. For example, one of the possible AMR technology applications is the management of commercial electrical power for reducing peak hour loads. Although there have been different rates to encourage off-peak-hour use of electricity for non-essential power consumption, implementations to take such an advantage have been very limited. This is because the physical control has to be implemented and maintained by the individual customers. If this responsibility can be shifted to a central facility under the utility company's control, there will be no need to train the customers for proper operation of the controls or to audit the compliances.
At this moment, the PSTN is the only natural candidate as the backbone to AMR applications. It possesses several essential ingredients which are crucial to the success of AMR. For example, it has reached almost any location where there is consumption of public utilities; it is capable of providing two-way communications at reasonable speeds with affordable cost; it has a unique characteristic of having the utility meters already correlated with the customers' telephone numbers by virtue of the business account records, avoiding the potential complexities in setting up new databases commonly associated with other techniques. Furthermore, this facility is constantly maintained by a regulated utility, the telephone company, to an established performance standard, thus simplifying much of the AMR operation procedures.
AMR has been utilizing PSTN for quite a few years, However, there is still an inherent limitation on using the telephone line for this purpose. Although a dedicated line would serve this purpose well, it is not economically practical. Thus, the AMR application has to be content with sharing the telephone line already existing on the customer premises. Since the telephone company central office automatically applies ringing signals to sound the bells in the telephone sets on every call without any distinction between the AMR or ordinary voice calls, the subscribers will be disturbed each time a utility company attempts to read the meter via the shared telephone line. This has been the obstacle that prevented a full acceptance of using the PSTN for the AMR application.
Initially, utility companies installed electronic readers at the customer sites that were set up to call in to the central equipment for reporting meter readings, thus the term "Inbound". This required each individual reader to have a certain level of sophistications such as automatic retrials upon encountering difficulties in contacting the central equipment, an electronic calendar clock to assure on-time reporting plus backup batteries to maintain its continuity in case of commercial power failures. In recent years, techniques have been developed such that utility companies can call out from a central equipment to poll the individual meters at any time, thus the term "Outbound". However, to avoid disturbing the customer during the meter reading sessions, the normal ringing signal has to be suppressed. One possible technique was disclosed in U.S. Pat. No. 5,010,568 issued to Merriam et al. on Apr. 23, 1991. Technically speaking, this method utilizes the "test trunk", sometimes referred to as "no ring trunk" facility of the telephone company central office that is originally equipped to support telephone maintenance and repair activities.
While such an approach is technically sound, it requires the telephone company to provide this capability by increasing the capacity of the test trunks as well as customizing the operating procedures for the calls originated by a meter reading equipment. Thus, this approach puts AMR at the mercy of the local telephone companies who may not be willing to cooperate. Besides, it will definitely cost the utility companies up-front investment capitals to set this facility up at each central office where there might be an AMR type of application, even if the telephone company goes along.
The communication protocol disclosed below allows the outbound AMR tasks be conducted in such a way that it follows the conventional telephone call procedures as well as utilizes only the existing network facilities. Consequently, the telephone company will not be required to provide any special support. Without telephone company's direct involvement, not only the initial capital investment cost is avoided but also allows the AMR service to be available to any isolated customers without geographical constraints.
It should be emphasized here that although the technique disclosed in this invention allows the practice of TRC through PSTN without ever involving the telephone company directly, the telephone company still benefits from this by having more completed calls than otherwise possible before the TRC is in service.